FYI, not all 4x5 enlargers will do 20x24. Using 35mm as a reference, because the short dimension is a convenient 1 inch.
The Omega D5 will only do up to 17.7x (covers 16x20). You would need to get the XL chassis, with the longer girder to get to 24x (covers 20x24).
The Durst L1000 will do 19x (not quite 20x24)

Or bolt the enlarger column to a bench/table with an adjustable height baseboard.